Spatial variability of environmental isotope and chemical content of precipitation in Jordan and evidence of slight change in climate

Abstract

The spatial variability of the δ18O and δD compositions of rain is attributed to variations in amount of precipitation (PPT), altitude effect, and air masses originating from different sources. Air masses that enter the area passing the Mediterranean Sea result in higher d-excess. The cold and dry continental air masses originating from the European continent come in contact with the warm Mediterranean Sea water, resulting in rapid evaporation and large scale convergence. The low d-excess value is less than 16 ‰ and associated with air masses that cross over the North African continent and controlled by a local orographic effect. The change in isotopic composition of δ18O in PPT with altitude is −0.15 ‰ per 100 m. A statistical model confirms that a slight decrease in annual average precipitation has occurred since 1988 and attributed to a minor change in climate. The current level of tritium in rain corresponds to the average level of tritium in the atmosphere. Rabba station recorded a twofold higher tritium concentration in 1995 than the other stations, which may be from leakage from a nuclear station in Israel. The chemistry of rainwater demonstrates a wide range of salinity (100–600 mg/l). The lowest solute concentrations are found at high elevations, and the highest solute concentrations are found in the eastern desert and the Jordan Rift valley. The salinity of rain is affected by desert dust, aerosols, amounts of PPT, and the direction of rain fronts. The aerosols and windblown soil are the most prevailing as the country is confined between three seas and the outcrop surficial geology is mainly sedimentary rocks.

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